Glomeruli in the kidneys showing a typical glomerulus and a scarred glomerulus

Focal segmental glomerulosclerosis (FSGS) results from scar tissue that develops in the glomeruli. Glomeruli are tiny structures within the kidney that filter waste products from the blood to create urine. A healthy glomerulus is shown on the left. When scar tissue develops in a glomerulus, kidney function gets worse (shown right).